1. Field of the Invention
The present invention relates to a water heating system, and more particularly, to an integral solar and heat pump water heating system wherein the coefficient of performance of the system is greatly improved by an active refrigeration cycle control using digital computer means.
2. Description of the Prior Art
Solar hot water systems have been gaining popularity in recent years because they utilize free solar energy. Refrigerant charged solar systems are of particular interest for their desirable efficiencies insofar as they employ latent heat transfer rather than sensible heat transfer. However, as evidenced in the U.S. Pat. Nos. 4,220,138 to Bottum, they require a backup heat source because they cannot attain usable water temperatures during winter seasons and because solar radiation is either unavailable or insufficient on rainy or cloudy days. Moreover, the heat transfer characteristic of the same is not optimized because of an inherent on-off control method for the refrigerant circulating pump means. Heat pump water heating systems are also enjoying a surge in popularity because of their compactness and efficiency. Solar assisted heat pump systems merit particular attention for their potential higher efficiencies. However, as disclosed in U.S. Pat. Nos. 4,226,604 to Weis and 4,302,942 to Charters et al, they also require a backup heat source because their capacity decreases at low ambient temperatures when the sun is not shining. The cost of installation is considerably higher than conventional heat pumps due to the expensive nature of solar collectors while the annual coefficients of performance are not significantly better as compared with the latter in that they operate at subambient temperature. The solar collectors are unglazed and are designed to derive heat energy from the surrounding air as well as from the sun's radiation.